Li-ion batteries have been adopted to date mainly as power sources for compact electronic instruments. Recently, the market of Li-ion batteries have been enlarged, and they have been considered as power sources for electric vehicles and medium- and large-scale commercial energy storage systems (ESS). However, in the case of medium- and large-scale rechargeable battery systems, safety and cost efficiency thereof are more important as compared to electrochemical performance thereof. In this context, Li-ion batteries have a certain limitation. Thus, there has been an increasing need for developing a rechargeable battery satisfying the above requirements.
As one of the plausible candidates satisfying the above requirements, a rechargeable magnesium battery which uses magnesium metal as a high-capacity capacity and high-safety anode material, while magnesium ions repeat reversible insertion and extraction into/from a cathode, has been paid increased attentions recently. Magnesium is much more cost-efficient, shows lower chemical activity than lithium, and furthermore, does not form any dendritic structure during the electrochemical deposition and dissolution process leading to an excellent safety. In addition, a rechargeable magnesium battery uses a metal directly as an anode, and thus has a significantly high capacity density per weight and volume corresponding to 2205 Ah/kg and 3833 Ah/L, respectively. Thus, magnesium is advantageous in various aspects.
However, in order to develop practical rechargeable magnesium batteries, it is still required to develop an electrolyte having a wide electrochemical potential window compatible with both a magnesium anode and a high-potential cathode material, and a high-potential and high-capacity cathode material which allows a reversible electrode reaction with magnesium ions. A typical magnesium cathode material developed to date, Mo6S8 Chevrel phase, has an energy density per weight just of 128 mAh/g, which is significantly lower as compared to the conventional cathode materials for a Li-ion battery. Moreover, it has a working voltage of about 1.2 V. Therefore, there is an imminent need for developing a novel cathode material.
However, most of electrolytes currently developed for a rechargeable magnesium battery have both high nucleophilicity and strong corrosive property derived from the incorporation of a high concentration of chloride ions (Cl−). Thus, it causes a side reaction with the conventional cathode materials (metal oxide (MOx), sulfur (S), selenium (Se) compounds) with ease, resulting in some disadvantages, including significant degradation of cycle characteristics or a limited potential window due to the decomposition of an electrolyte.
Under these circumstances, in order to develop high-capacity rechargeable magnesium batteries, it is required to develop a cathode material for a magnesium battery, which is stable chemically in the presence of such an electrolyte containing chloride ions, has strong anti-corrosive property capable of resisting the attack of chloride ions to overcome the above-mentioned limitation, shows higher capacity as compared to the conventional batteries, and provides cycle stability.